This invention relates to a hardware implemented system for inserting new instructions into a programmed set of instructions in memory in a functional sequencer. In a more specific aspect, the invention is related to a programmable logic controller having a keyboard module connected thereto in which there is provided a shift register for storage of new instructions and a counter in which the memory location at which the new instruction is to be placed is loaded and is counted down to zero beginning at the start of a memory cycle at which time the instruction in memory at the desired location is shifted into the shift register concomitantly with the shifting of the instruction from the shift register to memory followed by circulation through the shift register of all subsequent instructions stored in memory.
The present invention relates generally to devices known as programmable logic controllers. Controllers have heretofore been provided to control machines, processes, solenoids, motors, etc. Such controllers in general have a large number of output storage devices associated therewith, which devices are employed to connect power sources to machine elements or disconnect the same at times predicated upon conditions in the system and the relation of such conditions to a programmed set of instructions stored in a memory in the controller. Multiple relay installations have heretofore been employed to provide condition dependent control of machines or devices powered from alternating current sources. The installations have been made by guidance provided through electrical circuit diagrams in the form of ladder networks. Several attempts to solve problems encountered in simplifying installation procedures and operations are found in "Control Engineering", September 1972, page 45 et seq.
In the use of systems under direction of programmable logic controllers, it frequently becomes necessary to make physical changes in the system, adding more operative elements which must be controlled by the controller. In such controllers, or other functional computers, programmed sets of instructions ar stored within memory in response to which computations or sequences in the controller are directed. At times it, therefore, becomes necessary that the instruction set must be modified by adding an instruction somewhere in the programmed set.
In the computer art generally, the insertion of instructions in a programmed set has heretofore been carried out with software. The present invention provides a hardware insert function which allows more direct modification of the instruction set than with a separate software routine and in a manner uniquely and readily carried out without familiarity with conventional programming techniques.